The avian flu virus that occurs naturally in birds can be highly contagious among the species, but is rarely transmitted to humans. Common symptoms in humans include fever, cough, sore throat, eye infections, viral pneumonia, and other life-threatening complications. Doctors and scientists are working on vaccines to protect humans against H5N1 avian flu in case a pandemic occurs.
Avian influenza -- commonly called "bird flu" or "avian flu" -- is an infection caused by influenza (flu) viruses that occur naturally in birds. Wild birds can carry the virus, but usually do not get sick. However, some domesticated birds, including chickens, ducks, and turkeys, can become infected with the avian flu virus and die.
(Click Avian Flu Virus for more information about influenza viruses.)
H5N1 in Animals
One strain of avian flu, the H5N1 virus, is endemic in much of Asia and has recently spread into Europe. Avian H5N1 infections have recently killed poultry and other birds in a number of countries. Strains of avian H5N1 influenza may infect various types of animals, including wild birds, pigs, and tigers. Symptoms in birds and other animals vary, but virulent strains can cause death within a few days.
Avian flu H5N1 in humans is currently limited and not a pandemic. Human H5N1 influenza infection was first recognized in 1997, when this virus infected 18 people in Hong Kong, causing 6 deaths. Since 2003, more than 100 human H5N1 flu cases have been diagnosed in:
Of those cases, more than half have died as a result of the virus.
Currently, close contact with infected poultry has been the primary source of human infection for avian flu. Although rare, there have been isolated reports of human-to-human transmission. Genetic studies confirm that the influenza A virus H5N1 mutates rapidly, which means that should it adapt to allow easy human-to-human transmission, a pandemic could ensue. At this time, it is uncertain whether the currently circulating H5N1 virus will lead to a global disease outbreak in humans -- a pandemic.